1. Field of the Invention
The present invention relates to wireless communication methods, wireless communication systems, and wireless communication apparatuses.
2. Description of the Related Art
In a typical method for confirming a connection in a known small-scale network, an apparatus entering the network performs association processing with an apparatus functioning as a control station of the network, thereby enabling the apparatus to enter the corresponding network. After the association processing is completed, generally the apparatus is always regarded as being connected to the network. When the apparatus is disconnected from the corresponding network, disassociation processing is activated, thereby performing disassociation processing while recognizing the apparatus to be disconnected.
The association/disassociation processing is defined as an efficient method in a wired connection environment in which the existence of a terminal can be easily confirmed.
As a method for confirming an always-on access state, the control station of the network periodically exchanges predetermined information with each terminal, thereby sequentially monitoring the access state of each terminal.
Japanese Unexamined Patent Application Publication No. 11-251992 discloses the following method. In this method, a frame period is set to predetermined time, and connection links among all communication apparatuses in a network are confirmed using part of the frame period. Accordingly, a topology map of the overall network is constructed. The method described in Japanese Unexamined Patent Application Publication No. 11-251992 provides an area in which each communication apparatus forming the network sends a signal in each predetermined frame period. As long as each communication apparatus exists in the network, each communication apparatus sends a signal. Accordingly, the method can immediately detect a communication apparatus that no longer exists in the network.
FIG. 8 shows an example of a frame structure of a known connection confirmation method.
Referring to FIG. 8, a transmission frame period 45 is defined between a frame start packet (FSP) 41 and an FSP 43. Using a partial area of the frame period, each communication apparatus forming the network sends “connection confirmation information” to the control station. Accordingly, the connection status of each communication apparatus can be confirmed.
A station synch (SS) 42 and an SS 44 are divided into a plurality of small areas so that the connection confirmation information from each communication apparatus may not conflict with the other information. One small area is allocated to each communication apparatus. Each communication apparatus sends the connection confirmation information using the corresponding small area.
With this arrangement, all communication apparatuses send the “connection confirmation information” in each frame. If the frame period is short, such as a few milliseconds, the processing becomes redundant.
In the connection confirmation method in the known small-scale network, a communication apparatus that has completed association processing is regarded as being connected to the network. When the communication apparatus is disconnected from the network, the existence of the communication apparatus cannot be detected. Unlike a wired connection environment, it is necessary in a wireless connection environment to manage the existence of a communication apparatus by using a wireless connection. Thus, there is no means for the control station to easily detect the operating state of each terminal.
For example, a terminal station completes association processing and hence is regarded as being connected to the network. If for some reason the power supply to the terminal station is cut off, disassociation processing cannot be activated by the corresponding communication apparatus. Thus, the control station of the network cannot detect that the communication apparatus is disconnected from the network.
In order to solve this problem, as described in the foregoing Japanese Unexamined Patent Application Publication No. 11-251992, the following method is proposed. In, this method, the control station receives a signal transmitted on a relatively periodical basis from the terminal station. Having received the signal, the control station detects that the terminal station is connected to the network. In this method, a signal for confirming connection is required to be transmitted in each frame. If the frame period is set to a short period of time, such as a few milliseconds, the connection status is confirmed in each such short period. The connection confirmation in each such short period disagrees, in terms of time, with the time required for a human sense to determine connection/disconnection, which requires approximately a few seconds.
Generally, the known connection status confirming method confirms connection on the same periodical basis irrespective of the operating state of each communication apparatus forming the network. Thus, a sleeping communication apparatus must be activated on a predetermined periodical basis. In other words, the operating states of communication apparatuses forming the network differ from one communication apparatus to another. For a communication apparatus that does not need to transmit information, it is impossible to prolong a connection confirmation period in which connection confirmation is performed with the control station.